Numerous techniques and protocols exist for configuring networks to handle multicast traffic. For Internet Protocol (IP) and/or multiprotocol label switching (MPLS) implementations the existing solutions for multicast are based on multicast label distribution protocol (mLDP) or protocol independent multicast (PIM). These are all techniques that depend on a unicast shortest path first (SPF) computation followed by handshaking between peers to sort out a loop free multicast distribution tree (MDT) for each multicast source. At the same time numerous protocols exist that provide for unicast tunneling, and some (such as label based architectures like SPRING or MPLS-LDP implement a full mesh of unicast tunnels as an artifact for normal operation).
SPB is a protocol related to computer networking for the configuration of computer networks that enables multipath routing. In one embodiment, the protocol is specified by the Institute of Electrical and Electronics Engineers (IEEE) 802.1aq standard. This protocol replaces prior standards such as spanning tree protocols. SPB enables all paths in the computing network to be active with multiple equal costs paths being utilized through load sharing and similar technologies. The standard enables the implementation of logical Ethernet networks in Ethernet infrastructures using a link state protocol to advertise the topology and logical network memberships of the nodes in the network. SPB implements large scale multicast as part of implementing virtualized broadcast domains.
Proposals have been made to use global identifiers in the dataplane combined with the IEEE 802.1 aq technique of advertising multicast registrations in the interior gateway protocol (IGP) and using an “all pairs shortest path” computation to compute MDTs without the additional handshaking.
SPRING is an exemplary profile of the use of MPLS technology whereby global identifiers are used in the form of a global label assigned per label switched route (LSR) used for forwarding to that LSR. A full mesh of unicast tunnels is constructed via every node in the network computing the shortest path to every other node and installing the associated global labels accordingly. In the case of SPRING, this also allows explicit paths to be set up via the application of label stacks at the network ingress. Encompassed with this approach is the concept of a strict (every hop specified) or loose (some waypoints specified) route dependent on how exhaustively the ingress applied label stack specifies the path.
However, the configuration of flat multicast trees in such networks using MPLS, SPB, SPRING and similar technologies can generate a significant amount of state, in particular in association with source specific tree implementation of multicast groups. To implement a given multicast group it is necessary to install state to implement an MDT per source. Less optimal solutions exist such as spanning trees or shared trees, but a tree per source per group provides for efficient multicast delivery. Solutions for multicast also may involve protracted convergence due to handshaking and all involve excessive state in the network. The use of SPB or IEEE 802.1aq techniques permits accelerated convergence but does not address the volume of state problem, in particular in the case of large numbers of sparse multicast trees where the set of receivers for any given MDT is less than the set of network nodes. However, significant state remains to be maintained across the network. Further the use of SPB while providing for multipath between points in the network, cannot take advantage of the statistical improvements to load distribution available via techniques such as equal cost multipath (ECMP).